Oh the back, the back the back!! There was a period in my life where any girl sitting in front of me got at least a cursory back tickle. I tend to see tickling the back in 3 ways: skin, muscle and bone. Bone is really just the back ribs basically. I remember tickling an ex once, (she was on her back) and I kept walking my fingers further and further underneath her while she arched up and off the bed. It amused me partially because I had no idea if it was her back or the ribcage which caused the reaction. I asked. She said it was the ribs.
Folks who are particularly ticklish to massages, which tend to be a firmer touch, it's generally the muscles. I know a lady who would respond with machine gun giggles if your pressed near her right kidney. You could be massaging all over her back and as soon as the pressure hit that spot, she just erupted laughing. Funny thing though, she wouldn't move at all - and it wasn't as though it was unpleasurable for her. She just thought of it as a thing unique to her. "Oh yeah, that's my tickle spot. Just right there, don't worry about me laughing." I've heard massage therapists say the ticklishness is a sign of holding tension in that area. I'm sure that can be the case. I'm also sure it could sometimes just be ticklishness. When it's muscle sensitivity, normal massage pressure, heel of the palm, knuckles or an elbow can be effective. I recall once a lee facedown at a gathering who was reduced to a howling mass anytime an elbow point was applied under the shoulder blade.
Obviously, the skin of the back is some of the most sensitive on the body, and such a large canvas to play with. Drawing with fingers or a paintbrush is a lot of fun. A couple of things I've noticed about back tickling are quite interesting. 1) The muscle sensitivity thing seems to be more pronounced if one is standing or sitting, vs lying down prone. That's also my own personal experience receiving massages - the kneading doesn't tickles so much if I'm laying down flat. 2) I sort of just realized writing this, unlike most other tickle spots, I don't seem to recall ever hearing "stop", no matter how much it tickled, or how hard it made them laugh. Even where there was the involuntary pulling away, I can't recall a "stop, don't, no... etc". Continuously ticklinh the sides or underarms or knee squeeze or toes or neck (Not talking about an actual session here, just sort of casual) seem to invariably elicit such, but not the back! I believe more research is needed here! haha
